Teens Are Sleeping Less, and Smartphones Are Blamed

The authors find that sleep in teens fell after 2009, as smartphone use escalated. Lack of sleep has been linked to insulin resistance.

Today’s teens are getting less sleep than they need, and smartphones appear to be the reason, according to a new study from San Diego State University.

The researchers, reporting in the journal Sleep Medicine, examined data from 2 large government surveys of more than 360,000 teenagers that asked how frequently they got at least 7 hours of sleep, which is the minimum recommended for this age group; in fact, 9 hours is considered optimal. The study found that about 40% of teens in 2015 slept less than 7 hours per night; this share was 58% higher than 1991 and 17% higher than 2009.

Starting in 2009, the researchers found a sharp spike in smartphone use and a corresponding increase in the number of teens reporting 7 hours of sleep or less. What’s more, they saw that the more time teens spent on their smartphones, the less sleep they got: those who were online 5 hours a day were 50% more likely to get inadequate sleep compared with those online just an hour a day.

Lack of sleep has both short- and long-term consequences for teenagers. Those who get inadequate sleep might fall asleep in class, which can affect academic performance. And, more and more studies are finding connections between inadequate or disrupted sleep and insulin resistance, leading to higher rates of diabetes and cardiovascular disease.

“Teens’ sleep began to shorten just as the majority started using smartphones,” Jean Twenge, PhD, a professor of psychology at San Diego State and the study’s lead author, said in a statement. “It’s a very suspicious pattern.”

The researchers found that time spent on activities like homework, part-time jobs, or watching TV were stable or declined between 2009 and 2015, so they can’t be blamed for teens getting less sleep.

The need for sleep doesn’t disappear just because teens use smartphones or tablets late into the night, the researchers say. Teens simply end up napping on the weekends or catching up on sleep at other times of the day. The question is whether they are sleeping on a schedule that is good for their overall health.

It’s not just the time spent in front of screens that’s a problem. Other research shows that the glow of the screen interferes with circadian rhythms, making it harder to fall asleep once a device is turned off. That’s why sleep experts recommend shutting down electronics well ahead of bed time.

Twenge recommends limiting screen time for teens to 2 hours a day.

“Given the importance of sleep for both physical and mental health, both teens and adults should consider whether their smartphone use is interfering with their sleep,” she said. “It's particularly important not to use screen devices right before bed, as they might interfere with falling asleep.”